NdFeB system sintered magnet

Abstract

A NdFeB system sintered magnet produced by the grain boundary diffusion method and has a high coercive force and squareness ratio with only a small decrease in the maximum energy product. A NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (the “Dy and/or Tb” is hereinafter called R H ) attached to and diffused from a surface of the base material through the grain boundary inside the base material by a grain boundary diffusion treatment, wherein the difference C gx -C x between the R H content C gx (wt %) in the grain boundary and the R H content C x (wt %) in main-phase grains which are grains constituting the base material at the same depth within a range from the surface to which R H is attached to a depth of 3 mm is equal to or larger than 3 wt %.

The invention claimed is: 
     
       1. A NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (R H ) attached to and diffused from a surface of the base material through a grain boundary inside the base material by a grain boundary diffusion treatment,
 wherein a difference C gx -C x  between an R H  content C gx  (wt %) in the grain boundary and an R H  content C x  (wt %) in main-phase grains which are grains constituting the base material at a same depth within a range from the surface to which R H  is attached to a depth of 3 mm is equal to or larger than 3 wt %, and 
 a percentage of a total volume of a carbon rich phase in a rare-earth rich phase at the grain-boundary triple points in the base material to a total volume of the rare-earth rich phase is greater than 0% and equal to or lower than 50%. 
 
     
     
       2. The NdFeB system sintered magnet according to  claim 1 , wherein the NdFeB system sintered magnet has two opposite surfaces to which R H  is attached in the grain boundary diffusion treatment, and a thickness between the two surfaces is equal to or smaller than 10 mm. 
     
     
       3. The NdFeB system sintered magnet according to  claim 2 , wherein the thickness between the two surfaces is equal to or smaller than 6 mm. 
     
     
       4. The NdFeB system sintered magnet according to  claim 1 , wherein a carbon content of the entire base material is greater than 0 ppm and equal to or lower than 1000 ppm. 
     
     
       5. The NdFeB system sintered magnet according to  claim 1 , wherein an average grain size of the main-phase grains which are grains constituting the base material is equal to or smaller than 4.5 μm. 
     
     
       6. The NdFeB system sintered magnet according to  claim 1 , wherein the surface to which R H  is attached is a magnetic pole face.